Capacitors are electrical components that store electric energy. They function by having two conductive plates near each other but separated by an insulator known as a dielectric. To store a charge on a capacitor, one of the conductive plates is subjected to a voltage, forming an electrostatic field between the two conductive plates. As one plate collects a negative charge the other develops a positive charge. The ratio of the electric charge and the potential difference in voltage is called capacitance.
A typical self-capacitance sensor functions by measuring the change in capacitance of a system or capacitive loading when an external object comes near the driven conductive electrode in the system. If the external object is also a conductor, meaning it can conduct electricity, the capacitance of the system is changed and can be measured. The capacitance of the traces to the electrode sensor and the unwanted capacitance to ground cannot be distinguished from the wanted capacitance by the sensing circuit. When increasing the gain or electrode size, the effect of the parasitic capacitance is increased at the same rate as the desired capacitance. For self-capacitance electrodes the goal is to keep parasitic capacitance to a minimum and to maximize the size of the driven conducting plate. But as the size of the sensor is increased, the conductor is subject to increased electrical noise. Electrical noise can distort the sensing signal, making precise measurement or change in capacitance more difficult.